1. Field of the Invention
The present invention relates to the field of aqueous film coating of pharmaceutical, food, confectionery forms, and agricultural products, and is specifically concerned with providing coatings from a combination of a cellulosic polymer and lactose for coating such things as pharmaceutical tablets, pieces of candy, cereals, and agricultural seeds.
2. Description of the Prior Art
Film coating is a process of depositing a thin layer of material onto a substrate. Two goals of film coating substrates such as pharmaceutical tablets and the like are (1) to provide a functional protective barrier covering the outer surface of the substrate, and (2) to provide a pleasing appearance.
The process of film coating pharmaceutical, food, confectionery, and agricultural pieces usually involves rolling the pieces in a pan, or suspending the pieces on a cushion of air, and continuously spraying a fine mist of atomized droplets of a coating suspension onto the pieces, the droplets coalescing on the surface of the pieces to form a film coating.
Coating suspensions having an organic solvent are undesirable since these solvents are often flammable, often toxic, and hazardous to the health of film coating workers. Further, reclaiming organic solvent fumes, which are given off during spraying, from exhaust air ducting systems is expensive and often required by law.
Water-based coating suspensions are desirable to avoid the drawbacks of organic solvent-based coating suspensions. However, a major problem with aqueous coating suspensions is poor adhesion of the film to the substrate.